Fig. 18. A diagrammatic representation of the flow of electric current outward at the lens equator and inward at the anterior and posterior poles. The currents are thought to drive water flow along the same path. As described in the text, currents arise because of unequal spatial distribution of potassium channels, gap junctions, and Na, K-ATPase in the lens cell mass. For example, potassium channels are more abundant in the surface zones (S). Also, there are important differences between differentiating fibers (DF) and mature fibers (MF) in the way neighboring cells are coupled. (Baldo GJ, Gong X, et al: Gap junctional coupling in lenses from alpha (8) connexin knockout mice. J Gen Physiol 118:447, 2001)